This invention pertains to electrical scaling apparatus which uses an electro-optically scanned parabolic viewing mirror, and a pulse-generating and counting circuitry, for measuring and indicating the dimensions of an article, such as a log. In particular, it relates to such apparatus which includes means operable during scanning of the mirror's view for varying, in effect, the rate at which pulses generted in the apparatus are counted, so that a final count may be produced which is corrected for nonlinearity inherently encountered during scanning of such a mirror, and which is directly indicative of the desired dimension of the viewed article.
For the purpose of explantion herein, an embodiment of the invention is described in conjunction with the diametral scaling of logs traveling into a sawmill, and with the presenting of a visual display of obtained scaling information.
Modern sawmills have become, in many instances, highly automated operations in which decisions respecting the cutting of a log into lumber are often made automatically. These decisions must be made so as to obtain maximum economic benefit from each log, which normally means not merely getting the most available lumber out of the log, but more especially, getting the maximum number of boards of the most economically rewarding sizes.
Decisions regarding cutting in such a mill are usually made on the basis of automatic, multi-axial, diametral scaling of a log as it travels toward the saws in the mill--such scaling feeding information into a computer, or the like, which determines how the saws will be applied to the log. Logs moving toward the saws are typically viewed repeatedly, or continuously, from different angles to determine their dimetral dimensions in different planes, from which dimensionalinformation computer control is ultimately derived.
The present invention provides a scaling apparatus usable conveniently and accurately for making such measurements, and employing to this end a parabolic mirror for the purpose of viewing the dimensions of traveling logs. Such a mirror has the decided advantage of providing dimensional information which is independent of the mirror's distance from the viewed article, inasmuch as it provides at its focal point an image derived from rays received in parallel from the article. Operating at the mirror's focal point is a constant-speed, rotary, electrooptical scanner which scans the view of the mirror. As the scanner sweeps the mirror's view, and "sees" a log, pulsegenerating means in the apparatus operates to supply a counter with pulses whose final count is intended to indicate directly the log's diameter as viewed. Featured, importantly, in the apparatus is means which varies the effective rate at which pulses are counted, so as to "linearize" the summed count, whereby each counted pulse, essentially, represents substantially the same diametral distance of a viewed log.
Varying of this counting rate herein, and as will become apparent, may be accomplished either infinitely or in steps, and may be based either on a following of the actual angular position of the scanner, or upon an accurate assumption as to its position based upon the running count of pulses which is produced as the scanner sweeps the mirror's view. Disclosed herein as a preferred embodiment of the invention is apparatus in which the counting rate is varied in discrete steps rather than infinitely, with this varying being under the control of circuitry which "watches" the cumulative count of pulses during a scanning sweep of the scanner as an indication of the scanner's angular position. such an approach has been found to have cost advantages, and its use has been found to produce highly accurate and very acceptable results.
Various other objects and advantages which are attained by the invention will become apparent as the description which follows is read in conjunction with the accompanying drawings.